Your frame will snap from the weight of the real barrel. This is very expensive and not worth it.
Do not import real gun parts, let alone real machine gun parts, specially until you are 18 (or 21 for some States). Even then, you're asking for more attention than you need. "Why does he want a banned machine gun barrel? Does he have one?"
If you really must have real wood and such for your Marui tommy gun, go buy them from
www.marstar.ca (they are in Canada). You must be 18 to buy from there.
Still, you're wasting your cash.